WowWiki has info about how much experience you currently gain in AV:

http://www.wowwiki.com/Alterac_Valley#Experience_in_AV

COPIED:
All battlegrounds award experience when the team completes objectives. Experience gains are percentages based on the total experience needed to level for a player.

  • Destroying a tower or bunker awards roughly 1.16% of a level.
  • Defeating Galvangar or Balinda awards roughly 1.16% of a level.
  • Winning the match awards roughly 1.55% of a level.
  • Players are awarded an extra 0.38% for every remaining tower or bunker their team still has when the match is over, regardless of win or loss.


It is thus possible to gain 7.3% of a level from one match just by winning, and up to 8.8% for a win with all towers still up. It will take 14 wins to complete a level, or 18 losses, assuming your team destroys the four towers, and loses your four towers and kills Galvangar or Balinda.